Methods of making paper tissue, towel, and the like are well known, including various features such as Yankee drying, throughdrying, fabric creping, dry creping, wet creping and so forth. Conventional wet pressing processes have certain advantages over conventional through-air drying processes including: (1) lower energy costs associated with the mechanical removal of water rather than transpiration drying with hot air; and (2) higher production speeds which are more readily achieved with processes which utilize wet pressing to form a web. On the other hand, through-air drying processes have become the method of choice for new capital investment, particularly for the production of soft, bulky, premium quality tissue and towel products.
Fabric creping has been employed in connection with papermaking processes which include mechanical or compactive dewatering of the paper web as a means to influence product properties. See, U.S. Pat. Nos. 4,689,119 and 4,551,199 of Weldon; U.S. Pat. No. 4,849,054 of Klowak, and U.S. Pat. No. 6,287,426 of Edwards et al. Operation of fabric creping processes has been hampered by the difficulty of effectively transferring a web of high or intermediate consistency to a dryer. Further patents relating to fabric creping include the following: U.S. Pat. Nos. 4,834,838; 4,482,429 as well as 4,445,638. Note also U.S. Pat. No. 6,350,349 to Hermans et al. which discloses wet transfer of a web from a rotating transfer surface to a fabric.
In connection with papermaking processes, fabric molding has also been employed as a means to provide texture and bulk. In this respect, there is seen in U.S. Pat. No. 6,610,173 to Lindsay et al. a method for imprinting a paper web during a wet pressing event which results in asymmetrical protrusions corresponding to the deflection conduits of a deflection member. The '173 patent reports that a differential velocity transfer during a pressing event serves to improve the molding and imprinting of a web with a deflection member. The tissue webs produced are reported as having particular sets of physical and geometrical properties, such as a pattern densified network and a repeating pattern of protrusions having asymmetrical structures. With respect to wet-molding of a web using textured fabrics, see, also, the following U.S. Pat. Nos.: 6,017,417 and 5,672,248 both to Wendt et al.; U.S. Pat. No. 5,505,818 to Hermans et al. and U.S. Pat. No. 4,637,859 to Trokhan. With respect to the use of fabrics used to impart texture to a mostly dry sheet, see U.S. Pat. No. 6,585,855 to Drew et al., as well as United States Publication No. US 2003/0000664.
U.S. Pat. No. 5,503,715 to Trokhan et al. discloses a cellulosic fibrous structure having multiple regions distinguished from one another by basis weight. The structure is reported as having an essentially continuous high basis weight network, and discrete regions of low basis weight which circumscribe discrete regions of intermediate basis weight. The cellulosic fibers forming the low basis weight regions may be radially oriented relative to the centers of the regions. The paper may be formed by using a forming belt having zones with different flow resistances. The basis weight of a region of the paper is generally inversely proportional to the flow resistance of the zone of the forming belt, upon which such region was formed. The zones of different flow resistances provide for selectively draining a liquid carrier having suspended cellulosic fibers through the different zones of the forming belt. A similar structure is reported in U.S. Pat. No. 5,935,381 also to Trokhan et al. where the features are achieved by using different fiber types.
More generally, a method of making throughdried products is disclosed in U.S. Pat. No. 5,607,551 to Farrington, Jr. et al. wherein uncreped, throughdried products are described. According to the '551 patent, a stream of an aqueous suspension of papermaking fibers is deposited onto a forming fabric and partially dewatered to a consistency of about 10 percent. The wet web is then transferred to a transfer fabric traveling at a slower speed than the forming fabric in order to impart increased stretch into the web. The web is thereafter transferred to a throughdrying fabric where it is dried to a final consistency of about 95 percent or greater.
There is disclosed in U.S. Pat. No. 5,510,002 to Hermans et al. various throughdried, creped products. There is taught in connection with FIG. 2, for example, a throughdried/wet-pressed method of making creped tissue wherein an aqueous suspension of papermaking fibers is deposited onto a forming fabric, dewatered in a press nip between a pair of felts, then wet-strained onto a through-air drying fabric for subsequent through-air drying. The throughdried web is adhered to a Yankee dryer, further dried, and creped to yield the final product.
Throughdried, creped products are also disclosed in the following patents: U.S. Pat. No. 3,994,771 to Morgan, Jr. et al.; U.S. Pat. No. 4,102,737 to Morton; and U.S. Pat. No. 4,529,480 to Trokhan. The processes described in these patents comprise, very generally, forming a web on a foraminous support, thermally pre-drying the web, applying the web to a Yankee dryer with a nip defined, in part, by an impression fabric, and creping the product from the Yankee dryer. A relatively permeable web is typically required, making it difficult to employ recycle furnish at levels which may be desired. Transfer to the Yankee typically takes place at web consistencies of from about 60% to about 70%.
Conventional thoughdrying processes do not take full advantage of the drying potential of Yankee dryers because, in part, it is difficult to adhere a partially dried web of intermediate consistency to a surface rotating at high speed, particularly from an open mesh fabric where the fabric contacts typically less than 50% of the web during transfer to the cylinder. The dryer is thus constrained to operate at speeds below its potential and with heated air impingement jet velocities in the hood well below those employed in connection with conventional wet-press (“CWP”) technologies.
As noted in the above, throughdried products tend to exhibit enhanced bulk and softness; however, thermal dewatering with hot air tends to be energy intensive and requires a relatively permeable substrate. Thus, wet-press operations wherein the webs are mechanically dewatered are preferable from an energy perspective and are more readily applied to furnishes containing recycle fiber which tends to form webs with less permeability than virgin fiber. A Yankee dryer can be more effectively employed because a web is transferred thereto at consistencies of 30 percent or so which enables the web to be firmly adhered for drying.
Wet press/wet or dry crepe processes have been employed widely as is seen throughout the papermaking literature as noted below. Many improvements relate to increasing the bulk and absorbency of compactively dewatered products which are typically dewatered in part with a papermaking felt.
U.S. Pat. No. 5,851,353 to Fiscus et al. teaches a method for can drying wet webs for tissue products wherein a partially dewatered wet web is restrained between a pair of molding fabrics. The restrained wet web is processed over a plurality of can dryers, for example, from a consistency of about 40 percent to a consistency of at least about 70 percent. The sheet molding fabrics protect the web from direct contact with the can dryers and impart an impression on the web.
U.S. Pat. No. 5,087,324 to Awofeso et al. discloses a delaminated stratified paper towel. The towel includes a dense first layer of chemical fiber blend and a second layer of a bulky anfractuous fiber blend unitary with the first layer. The first and second layers enhance the rate of absorption and water holding capacity of the paper towel. The method of forming a delaminated stratified web of paper towel material includes supplying a first furnish directly to a wire and supplying a second furnish of a bulky anfractuous fiber blend directly onto the first furnish disposed on the wire. Thereafter, a web of paper towel is creped and embossed.
U.S. Pat. No. 5,494,554 to Edwards et al. illustrates the formation of wet press tissue webs used for facial tissue, bath tissue, paper towels, or the like, produced by forming the wet tissue in layers in which the second formed layer has a consistency which is significantly less than the consistency of the first formed layer. The resulting improvement in web formation enables uniform debonding during dry creping which, in turn, provides a significant improvement in softness and a reduction in linting. Wet pressed tissues made with the process according to the '554 patent are internally debonded as measured by a high void volume index. See, also, U.S. Pat. No. 3,432,936 to Cole et al. The process disclosed in the '936 patent includes: forming a nascent web on a forming fabric; wet pressing the web; drying the web on a Yankee dryer; creping the web off of the Yankee dryer; and through-air drying the product; similar in many respects to the process described in U.S. Pat. No. 4,356,059 to Hostetler.
It has been found in accordance with the present invention that the absorbency, bulk and stretch of a wet-pressed web can be vastly improved by wet fabric creping a web, while preserving the high speed, thermal efficiency, and furnish tolerance to recycle fiber of wet-press technology by way of operating the process under conditions operative to rearrange an apparently randomly formed wet web.